The present invention relates to an electron beam device comprising an evacuated envelope formed by optically transparent faceplate, a conical portion and a neck, an electron gun within the evacuated envelope comprising a tubular body of an insulating material in which there are provided some generally cup-shaped electrodes and an electrical connection to at least one cup-shaped electrode carried by the wall of the tubular body.
In the present specification the term electron beam device is to be understood to include cathode ray tubes, X-ray tubes, electron beam lithography apparatus, scanning and transmission electron microscopes, electron guns for scanning Auger mass spectrometers and also ion guns (not an electron beam discharge device within the normal meaning of the term). For convenience of description, the electron beam device will be described with reference to a cathode ray tube.
European Patent Application No. 86200481.9 discloses a cathod ray tube having an electron gun consisting of a vitreous tubular envelope formed by heating and drawing under reduced pressure onto a bipartite, profiled suction mandril. An end portion of the tubular body has a plurality of steps of decreasing radius. The steps form abutments or reference surface against which drawn, cup-shaped form abutments or reference surface against which drawn, cupshaped metal electrodes bear. The metal electrodes are of a sufficiently thin material that they can adapt to the cross-section of the stepped portion into which it is received. At least the terminal portions of the electrical connections to some of the drawn metal electrodes, namely those which cannot have a lead-out through the open end of the tubular body, are held captive in the wall of the tubular body. A main focusing lens is formed by a helix of an electrically resistive material to which electrical connections are made.
A problem which can occur with electrical connection(s) to the cup-shaped metal electrode(s) is that when deep drawing these electrodes, the skirted portion, the lip of which bears against the surface of the stepped portion, is conical rather than truly cylindrical. As the electrical contact between the terminal portion of a lead-out and the electrode is essentially a point-contact, then in an extreme case the conicity of the skirted portion may be such that the point-contact is not established. This problem can be very inconvenient because unless the fault can be rectified it may mean discarding the complete electron gun. Since the insertion of the cup-shaped electrodes is in the final phase of manufacture, which phase has been preceded by the more expensive operation of providing a resistive layer in the main focusing part of the electron gun, which layer is scored to provide the helical main focusing lens, then discarding a completed electron gun is costly.